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Incandescent bulbs produce light when an electric current passes through a filament
and causes it to glow. Because they are less energy efficient than other light sources, they are best used for task lighting that demands high levels of brightness.
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Fluorescent bulbs produce light when an electric arc passes between cathodes to
excite mercury and other gases producing radiant energy, which is then converted to visible light by a phosphor coating.
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High-Intensity Discharge (HID) bulbs produce light when an arc passes between cathodes
in a pressurized tube, causing metallic additives to vaporize. They have long lives and are extremely energy efficient, but - with the exception of metal halides - they do not produce pleasing light colors. In residential settings, HIDs are most often used for outdoor security and area lighting.
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Light Emitting Diodes (LEDs) produce light when voltage is applied to negatively
charged semiconductors, causing electrons to combine and create a unit of light (photon). In simpler terms, an LED is a chemical chip embedded in a plastic capsule. Because they are small, several LEDs are sometimes combined to produce a single light bulb.